1. Field of the Invention
The present invention relates to an anti-theft circuit, and more particularly, to an anti-theft circuit for a portable device, in which a correlation in a PN(Pseudo Random Number) sequence is employed for effective prevention of a portable device from being thieved.
2. Background of the Related Art
FIG. 1 illustrates the steps of an exemplary generation of a general pseudo-random number sequence, with three bits of a delay bit size. If initial values of the delay bits are xe2x80x981 0 0xe2x80x99, delay bits are shifted to repeat in an order of 0 0 1, 0 1 0, 1 0 1, 0 1 1, 1 1 1, 1 1 0, with a period of 23xe2x88x921, i.e., 7 chips. The pseudo-random number sequence generated in this case is xe2x80x981 0 0 1 0 1 1xe2x80x99, which is repetitive.
As an exemplary related art anti-theft circuit, a car anti-theft circuit will be explained with reference to the attached drawings. FIG. 2 illustrates a block diagram of a transmission system in the related art anti-theft circuit, and FIG. 3 illustrates a block diagram of a reception system in the related art anti-theft circuit.
The related art car anti-theft circuit is provided with electrical systems in a car, a controller disposed between electrical components in each of the electrical systems and a power supply block, and a transmitter for transmitting an activating signal to the controllers. The controllers are supplied of power from the power supply block in the car. The controller maintains its power path to the electrical component cut-off until the controller receives an encoded and transmitted activating signal when the controller decodes and compares to a value stored in advance, to establish a power supply path and put the electrical component into regular operation if the value is same. When the encoded, and transmitted signal is not the same as the value stored in the controller under an irregular condition, the power supply path to the electrical component is not established. As a result, the electrical component is not put into regular operation, allowing a theft prevention signal to be transmitted from the transmitter with a signal of an audible frequency band or a low powered FM system signal.
The transmission system in the aforementioned related art car anti-theft circuit has a system as shown in FIG. 2.
Referring to FIG. 2, the transmission system is provided with a power supply block 11, a switching block 12 for switching a power supplied from the power supply block 11, an encoder 13 for encoding a particular signal upon reception of the power under the switching of the switching block, and a transmitter 14 for transmitting the signal encoded in the encoder 13.
FIG. 3 illustrates a reception system in the car anti-theft circuit.
Referring to FIG. 3, the reception system in the car anti-theft circuit has a voltage regulating unit 22 for regulating a voltage level supplied from a power supply unit 21, a receiver 23 disposed between the electrical systems in the car for receiving the activating signal transmitted from a transmitter 22 in the transmission system, a decoder/comparator unit 24 for decoding the activated signal received through the receiver 23 and comparing to a value stored in advance, and a switching block 25 for selectively switching a voltage in the voltage regulating unit 22 according to a result of comparison in the decoder/comparator unit 24. In the car anti-theft circuit having the transmission system and the reception system, a particular active signal is transmitted and sensed, to cut off a power supply circuit selectively in an action of theft prevention of a car.
However, because the related art anti-theft device should encode and decode a particular signal, for making an anti-theft action according to a result of the comparison, the related art anti-theft device requires a decoding block, and can not provide a particular signal source.
Accordingly, the present invention is directed to an anti-theft device for a portable device that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide an anti-theft circuit for a portable device which can effectively prevent a portable device from being thieved.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the anti-theft circuit for a portable device, in which a correlation in a PN(Pseudo Random Number) sequence is employed for effective prevention of a portable device from being thieved by issuing an alarm when a portable device is out of preset range which causes a difference of a time offset in the PN sequence, includes a transmission block disposed in the portable device having a block for generating a particular pseudo random number sequence and a multiplication block for always multiplying a xe2x80x98highxe2x80x99 value to an output of the block for generating a particular pseudo random number sequence, the transmission block for converting an output of the multiplication block into an analog value and transmitting the analog value, and an anti-theft sensing circuit separate from the portable device for receiving a signal transmitted form the transmission block, sampling the signal, multiplying a sampled value to a pseudo random number sequence identical to a case of the transmission block, summing for a time period, comparing to a preset threshold value, and selectively providing an alarm signal to outside thereof according to a result of the comparison.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.